Existing methods for oil removal are based on techniques such as filtration, gravity separation, biological treatment methods, and induced floatation. Other approaches include API (American Petroleum Institute) separators, developed for handling refinery wastewaters, dissolved air flotation oil-water separators, induced air flotation oil-water separators, carbon adsorption and ultrafiltration treatments.
One existing technique employs a coalescing medium, such as, for instance, that supplied by Lantec Products (www.lantecp.com) under the name of HD Q-PAC. In a specific application for removing oil from storm water in a power plant, a unit using HD Q-PAC material was designed to handle 1900 gallons per minute (gpm) of water with an oil concentration of 4250 milligrams/liter (mg/l).
A coalescing system is also supplied by Pall Corporation of East Hills, N.Y. under the name of AquaSep® Plus. In the Pall AquaSep Plus Liquid/Liquid Separation System with Coalescer in a Horizontal Housing, illustrated in FIG. 2 of Pall Corporation Data Sheet GAS-4105g, available at www.pall.com, coalescer elements are stacked horizontally on top of a separator element. The purpose is to ensure equally distributed flow through the separators. After the separator elements, a settling zone is provided for the separation of the two liquid phases. The pressure drop through this system is 2 pounds per square inch differential psid) when new and it has to be replaced when the pressure drop reaches15 psid.
Many water treatment methods, such as, for instance, reverse osmosis or ultrafiltration require pre-treatment of the contaminated water, adding to overall wastewater treatment costs.
While filtration generally provides good oil removal, capacity and energy consumption have to be considered when designing filtration systems. Since filter media have a given permeability, determining the resistance of the medium for contaminated water flowing through it, this property, commonly monitored by the pressure drop across the filter material, generally increases as the filter becomes saturated with contaminants. As a result, either the amount of water passing through the filter has to be reduced or the pumping power has to be increased leading to a reduction in efficiency from an energy standpoint.
The most commonly used material for removing organic compounds from liquids and gases is activated carbon. Activated carbon is highly porous and thus provides large internal surfaces for adsorbed molecules to reside. However, purification methods based on adsorption by activated carbon as well as other purification techniques such as reverse osmosis and ultrafiltration strongly depend on temperature and their removal capacities and/or efficiencies may be affected under operating temperatures higher than ambient.
Organoclays such as bentonite modified with quaternary amine cations, also can be used to remove oil from water and they are particularly suitable for removal of large organic molecules of low solubility. One of these clay-based products is sold by Biomin (www.biomininc.com) under the name of OilSorbrm. In many cases, a packed bed of organoclay granules is used before the activated carbon to improve its adsorption efficiency, since activated carbon can quickly be blinded by oils that clog its porous surface.
U.S. Pat. No. 6,709,600 B2 issued to Hrubesh et al. on Mar. 23, 2004, the teachings of which are incorporated herein by reference in their entirety, discloses adsorption capacity of hydrophobic silica, aerogel for toluene, cyclohexane, trichloroethylene and ethanol from aqueous solutions.